Indexing device for drafting instrument

ABSTRACT

An indexing device for drafting instruments is described wherein index movements may be obtained with direct manipulation of the drafting head of the instrument. Variable index spacings are obtained with a compound pawl acting on a ratchet wheel or member. The compound pawl is formed of individually adjustable pawl elements. In an alternate embodiment variable index spacings are obtained by changing the speed ratio coupling effective between the ratchet wheel and the drafting head. The speed ratio coupling may be varied continuously or in discreet steps. Several embodiments are described including a drafting head for dividing a line into a desired number of spaces utilizing an index device according to this invention.

1 United States Patent 1 1 3,762,055

Citrin Oct. 2, 1973 [54] INDEXING DEVICE FOR DRAFTING 739,955 ll/l932 France 33/[10 INSTRUMENT [75] Inventor: Paul Stuart Citrin, New Milford, Pnmary Harman Conn Attorney-Louis H. Reens [73] Assignee: Sieburg Industries Incorporated, [57] ABSTRACT Danbury, Conn. An indexing device for drafting instruments is de- [22] July 1971 scribed wherein index movements may be obtained [21 A l N 162,909 with direct manipulation of the drafting head of the instrument. Variable index spacings are obtained with a compound pawl acting on a ratchet wheel or member. [52] US. Cl. 33/81 The compound p is formed of individually j [5 1] III!- CI B43I 13/24 able p elements In an alternate embodiment vari Field of Search 33/81, 40 able index p i g are obtained y g g the Speed ratio coupling effective between the ratchet wheel and [56] References Cned. the drafting head. The speed ratio coupling may be var- UNITED STATES PATENTS ied continuously or in discreet steps. Several embodi- 2,675,619 4/1954 Cone 33/81 x men s are e ri d including a drafting head for divid- 705,473 7/l902 Sternfeld 33/110 ing a line into a desired number of spaces utilizing an FOREIGN PATENTS OR APPLICATIONS index device according to this invention.

406,816 7/1944 Italy 33/81 29 Claims, 28 Drawing Figures PAFEMEW 3.762.055

INVENZTZYR' Siam r (4 inn RTTORNEY.

PAIENTEDUBT 2191a SHEET 3 (IF 6 [NVbfA/TQR M12 Paul film/"i (dun BY 5 i W I W TTORNEY INDEXING DEVICE FOR DRAFTING INSTRUMENT FIELD OF THE INVENTION This invention relates to a line indexing device for drafting instruments to form regularly spaced lines such as for sectioning, cross hatching, line dividing, and the like.

BACKGROUND OF THE INVENTION Index devices for drafting instruments have been known for many years. Typically, an index device is coupled to move a drafting head with incremental intervals over a flat surface on which a drawing to be worked is located. The U.S. Pat. to Moller, No. 1,362,635, for example, describes an index device wherein a ratchet wheel is mounted to the drafting head, such as a T square. A pawl is applied to rotate the ratchet wheel a distance determined by the angular spacing between index stops located on the ratchet wheel. The pawl is manually actuated to produce a linear incremental movement of the drafting head.

The parallel liner apparatus described in the U.S. Benton Pat. No., 1,066,576, employs a replaceable spindle with regularly spaced notches that are engaged by a pawl to produce incremental drafting head movements when the pawl is actuated.

In the U.S. Pat. to Cone, No. 2,675,619, an index device is described wherein three different ratchet index wheels are coaxially mounted for rotation in correspondence with movement of the drafting head. A rotatably movable pawl is mounted for selective engagement with any one of the three ratchet wheels to provide successive index positions of the drafting head in cooperation with selectively spaced stops mounted on the drafting head. The pawl is manually actuated to move the drafting head with predetermined intervals.

The parallel ruling apparatus described in the U.S. Pat. to Shelley, No. 3,025,604, advances a drafting head by rotating a manual control knob. The control knob rotates a lead screw which in turn controls the position of the drafting head. Line spacings are selected with the use of indicia associated with the control knob or audible clicks from a detent device.

A disadvantage of the described prior art index devices resides in their cumbersome design. For example, the Shelley index device employs elaborate gearing to advance the drafting head with complex releasing elements for use of the drafting head without indexing. Furthermore, these described prior art devices do not enable the operator to obtain index movements with direct manipulation of the drafting head.

SUMMARY OF THE INVENTION With an index apparatus in accordance with the invention, precise index movements are obtained by directly advancing the drafting head in one direction for an interval which is gauged such as by listening for an audible click from a spring loaded pawl or by sightdistance judgment and then reversing the drafting head in an opposite direction until a positive index stop is encountered when the pawl seats against an index stop on a ratchet member. This direct manipulation of the straight edge located over the drawing enhances drawing control and facilitates the ruling of many parallel lines for sectioning, cross hatching or the like.

An index apparatus made in accordance with the invention and as described herein employs a ratchet wheel driven into rotation by means of a flexible cable which is coupled to the drafting head. The ratchet wheel is provided with index stops distributedabout the axis of rotation of the ratchet wheel. The index stops freely pass a pawl when the ratchet wheel is rotated in one direction but provide successive index stops, both for the wheel and the drafting head when the ratchet wheel is rotated in the opposite direction. The drafting head may thus be moved with successive index positions by advancing the head from a desired reference line along a direction which rotates the index stops freely past the pawl and then reversing the movement of the head to seat the pawl against an index stop. A release mechanism is employed, whereby the operative position of the ratchet wheel and its index stops relative to the drafting head becomes adjustable so that indexing may be commenced from any desired point on the drafting table. This method of generating index lines is advantageously suited for the draftsman whose concentration and manual control may remain focused directly on the drawing surface.

An advantageous feature of an index apparatus in accordance with the invention includes a compound pawl having a number of pawl elements which may be selectively moved to engage index stops on the ratchet wheel. One or several pawl elements may be actuated to provide a programmed line spacing with alternate long and short spaces.

The index apparatus of this invention employs conveniently located release devices which enable the operator to commence index spacing from any desired reference point. One release device is operative to sufficiently reduce tension in a connecting cable drive to enable the operator to manually override the index device and position the drafting head at a desired location. Another embodiment includes a releasable friction disc coupling between the index device and the drafting head.

Another feature of an index apparatus of this invention provides for a continuously adjustable line spacer. A continuously variable drive ratio is obtained so that the line spacings determined by the index stops on a ratchet wheel may be effectively increased or decreased by varying the drive ratio.

The programmable feature of an index device of this invention may be advantageously employed to divide a line into any desired number of equal spaces, A straight edge on the drafting head is provided with indicia which spatially correspondwith the index spacings obtained with an acutated pawl element. A simple drafting procedure may then be employed to divide a line into the desired number of parts. Non-equal spacings or spacings which relate to a complex mathematical relationship such as harmonic, parabolic, etc. may be obtained.

The components utilized with an indexing device in accordance with the invention lend themselves to accurate design for precision index movements for professional drawings. Accuracy of index lines or index positions of the drafting head is particularly desirable when the drawing is to be reduced to generate precision photographic working plates.

It is, therefore, an object of this invention to provide an apparatus for indexing a line former such as a drafting head in a convenient accurate manner.

It is a further object of the invention to provide an in ex apparatus of relatively few components that may be conveniently incorporated with drafting instruments to provide a versatile and flexible line spacing control with a wide variety of programmable index movements.

These and other advantages and objects may be further understood with reference to the following description of several embodiments of the invention in conjunction with the drawings.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a partial perspective view of a drafting table utilizing an index apparatus in accordance with the invention.

FIG. 2 is a partial perspective exploded view of an index apparatus in accordance with the invention.

FIG. 3 is a partial horizontal top broken away view of the assembled index apparatus shown in FIG. 1.

FIG. 4 is a section view of a control module in an index apparatus of this invention and is taken along the line 4--4 in FIG. 3.

FIG. 5 is a section view of a program control and is taken along the line 55 in FIG. 3.

FIGS. 6-10 are different side views in elevation of a cam employed with the program control in an index apparatus of this invention.

FIG. 10A is a section view of the cam taken along the line l0A-l0A in FIG. 6.

FIG. 1 l is a perspective exploded view of an alternate embodiment of a ratchet program wheel for use with a programmable index apparatus in accordance with the invention.

FIG. 12 is a section view of another embodiment of a control module employed with an indexing apparatus in accordance with the invention.

FIG. 13 is a perspective view of a ratchet program wheel and a compound pawl utilizing pawl elements of different lengths for use with an indexing device in accordance with the inventions.

FIG. 14 is a perspective view of still another embodiment for a program control for use with an index apparatus in accordance with the invention.

FIG. 15 is a vertical schematic presentation of the ratchet program wheel employed with the embodiment shown in FIG. 2.

FIG. 16 is a partial top plan view of the ratchet wheel employed in the embodiment of FIG. 2.

FIG. 17 is a schematic presentation of an alternate embodiment for an indexing device in accordance with the invention.

FIG. 18 is a top plan view of a scale or drafting head for dividing a line into equal spaces with an indexing device in accordance with the invention.

FIGS. 19, 20, and 22 are schematic presentations of the drafting head of FIG. 18 at various intermediate positions thereof during a division of a line into equal spaces.

FIGS. 21 and 23 are plan views of drawing lines generated while dividing a line into equal spaces utilizing the drafting head of FIG. 18.

FIG. 24 is a vertical section view of another embodiment of a control module for an indexing apparatus to provide variable line spacing.

FIG. 25 is a schematic presentation of an operationreversing device for use with an index apparatus in accordance with the invention.

FIG. 26 is a broken perspective view of still another embodiment for a programmable index device in accordance with the invention.

FIG. 27 is a broken perspective view of a program index shaft for use with the embodiment shown in FIG. 26.

DETAILED DESCRIPTION OF EMBODIMENTS With reference to FIG. 1 a drafting instrument 20 is shown located on a conventional drafting table 22 having a drawing surface 24 on which a work sheet 26 or drawing paper is located. The drafting instrument 20 includes a straight edge or drafting head 28 formed of X and Y edges 29'29 respectively and of conventional design. The drafting head 28 is mounted for orthogonal movement along perpendicular X-Y directions in a manner that is well known in the art.

The drafting head 28 is supported by a Y-beam 30 along which the drafting head 28 is movable along a track and balanced by a conventional balanced-cable device (not shown). The Y-beam 30 in turn is mounted for movement along the X direction on an X-beam 32 also in a manner that is well known in the art. The drafting head 28 further may be angularly rotated with a conventional protractor mounting 34 about an axis 36.

An index device 40 is mounted on the Y-beam 30 and includes a control module 41 and a longitudinal channel shaped housing 42 which spans the length of the Y-beam 30 so that the drafting head 28 may be indexed anywhere along the Y direction of table surface 24. The channel 42 (and module 41) houses a continuous cable loop 43 which is operatively connected to the drafting head 28 by means of a bracket 44. The control module 41 may be integrally mounted within the Y beam 30 for operative contact with a cable employed therein for balance of the drafting head. In such case, the bracket 44 would connect to the cable in the Y beam 30 and the channel 42 can be eliminated.

A release lever 46 is operatively connected in series with the loop 68 in channel 42 to control the cable tension. In one position, lever 46 reduces cable tension sufficiently to permit manual overriding of the index device 40. The draftsman may then move the drafting head 28 along the Y direction to any desired position where the lever 46 is moved to increase cable tension to bring the index device 40 into operation. In this manner index spacing may be conveniently referenced from any point on surface 24. When lever 46 is in tension release position, the cable tension is still sufficient to enable indexing, though the index stops may be manually overridden with appropriate manipulation of the drafting head 28.

The control module 41 is located at the lower end of channel 42 and is provided with a program dial 48 by which index spacings may be selected and varied index intervals may be programmed. As illustrated on the drawing sheet 26 in FIG. 1 a number of section lines have been drawn on sheet 26 with different sized spacings 52 and 54 between section lines 56.1-56.2 and 56.2-56.3. This pattern may be conveniently repeated as illustrated by controlling the drafting head 28 as may be appreciated from the following description of FIG. 2. Regular spacings of lines such as at 57 may also be obtained.

In FIG. 2 the control module 41 is shown including a ratchet program wheel 62 formed of a plurality (four in the embodiment of FIG. 2, though fewer or more could be used) of axially spaced ratchet plates 64 separated by spacer discs 65. Each ratchet plate 64 is provided with index stops 66 cut into peripheral edges of the ratchet plates 64. A compound pawl 68 is shown mounted for operative engagement with the index stops 66. The compound pawl 68 includes a plurality of pawl elements 70.1, 70.2, 70.3 and 70.4, each of which is disposed opposite a ratchet plate 64 to contact its associated index stops 66. A cam 72 is mounted adjacent the compound pawl 68 and has cam surfaces sized and shaped to respectively control the movement of each of the respective pawl elements 70 towards a ratchet plate 64. The cam 72 is mounted for rotation about a vertical axis 74 and is provided at its upper end with the manually movable program control wheel 48.

As shown in FIGS. 2, 3 and 4, the ratchet wheel 62 is mounted for rotation about a bearing shaft 76 to which a bearing 78 is connected. A pulley 80 is coaxially mounted over the bearing 78 and cable 43 is wrapped around the pulley 80. The ratchet wheel 62 is pressed onto a shaft 82 to which a control knob 84 is also affixed by means of a set screw 85 (see FIG. '4). The shaft 82 is provided with a bore 87 sized to freely receive the stationary bearing shaft 76. The assembly formed by knob 84, shaft 82 and ratchet wheel 62 releasably seat coaxially with the bearing shaft 76 on a friction coupling to effectively connect to the cable 43. The friction coupling is formed of a pair of annular friction discs 86-86. One friction disc 86' is mounted to the underside of ratchet wheel 62 (See FIG. 4) and the other annular friction disc 86 is mounted coaxially with and on the outer race of bearing 78. The ratchet wheel 62 may thus be axially removed by lifting it with knob 84 from the lower friction disc 86 for replacement or to enable the operator to move the drafting head without index action. The bearing shaft 76 provides coaxial guidance of the shaft 82 and could be eliminated with cap 144 providing adequate coaxial location to assure engagement between annular friction discs 86-86'.

As illustrated in FIG. 2 each ratchet plate 64 is formed with peripherally located index stops such as 66. The index stops 66 are oriented counterclockwise to each operatively provide a stop edge 90 which seats against a pawl element 70 upon counterclockwise rotation as indicated by arrow 92. The ratchet plates 64 are axially spaced from one another of spacers 65 to place their index stops 66 in alignment with the ends, such as 94, of pawl elements 70. Pawl elements 70 as shown are formed from a common resilient spring material to form compound pawl 68 which has one end 96 affixed to the module housing 98 with suitable screws 100 to effectively support the pawl elements in cantilever fashion. The compound pawl 68 is so oriented that the pawl elements 70 normally are spaced from the index stops 66 but may be selectively urged towards the index stops 66 by cam 72. The pawl elements 70 need not be made from a common plate, but may be individual resilient strips.

The cam 72 is mounted adjacent the pawl elements 70 and has a peripheral cylindrically shaped cam surface, which when rotated opposite a pawl element 70, urges that pawl element towards the cam stops 66 on a ratchet plate 64. The cam 72 is further provided with recessed cam surfaces at different angular locations such as 104.1 and 104.2. When a recessed cam surface 104 is rotated opposite the compound pawl 68 those pawl elements 70, which are opposite this recessed cam surface 104, will remain in their normal position, i.e. away from the index stops 66 of a ratchet plate 64. On the other hand, those pawl elements, which are opposite a cylindrical cam surface will be urged towards the index stops 66 of a ratchet plate. In this manner, depending upon the axial location of the recessed cam surfaces 104 and the angular position to which cam 72 is rotated, one or several pawl elements may be actuated to provide programmable indexing of drafting head 28.

The variable line spacings (as shown in FIG. 1) obtainable with the index apparatus of FIG. 2 utilizes the cooperative relationship between the index stops 66 on the ratchet plates 64 and the ends 94 of the cantilever mounted pawl elements 70 which seat against edges of the index stops. In the control module embodiment shown in FIGS. 2 and 3 the ends 94 of the pawl elements 70 all terminate along a common line while the index stops 66 on respective ratchet plates 64 are angularly offset from one another.

FIG. 15 illustrates how the ratchet plates 64.1, 64.2, 64.3 and 64.4 are oriented relative to one another. The ratchet plates 64 are identical in shape, but are angularly offset to provide relative positions of their index stops in a manner as shown in FIG. 15.

Suppose, for example, that the lower pawl elements 70.4 and 70.3 have been actuated by cam 72. In such case the index movements of ratchet wheel 62 are, as shown in FIG. 16, of different arcuate distances 106 and 108. The non-equal line spacing illustrated in FIG. 1 may thus be obtained.

FIGS. 6 through 10 and 10A illustrate the various cam surfaces employed. Cam 72 is provided with five different angularly spaced cam faces which are respectively illustrated in FIGS. 6 through 10. Each cam face has a generally rectangular region such as 110, the shape of which is determinative of the pawl element that is to be actuated. This region 110 is shown in dotted outline in FIG. 6 and extends along the rotational axis 74 of cam 72 to span the full height h occupied by the pawl elements 70. The region 110 may be provided with recess recesses such as 104.1 in FIG. 7 to correspondingly deactivate the pawl elements 70.2 and 70.3 located at the same height. Thus the cam surface in FIG. 6 possesses no recesses and when rotated opposite the pawl elements 70 urges each towards a ratchet plate 64 as suggested by the pawl element numbers listed below cam 72. The cam face in FIG. 7 has a recess 104.1, which is sized to receive both pawl elements 70.2 and 70.3 while the remaining pawl elements 70.1 and 70.4 are actuated towards index stops 66 on ratchet plates 64.1 and 64.4 respectively. The cam face in FIG. 8 has a recess 104.2 which extends over the full height h of the pawl elements 70 to receive all. Hence, when cam surface 104.2 is rotated opposite. the pawl elements, none is actuated and no index action is available and the drafting head 28 may be moved without indexing. The remaining cam faces 104.3 and 104.4 are shaped in a similar manner to provide different index programs. The cam 72 is conveniently rotated to program positions with the thumb wheel 48 which is affixed to the upper segment of cam 72. A detent 112 (FIG. 5) is located to cooperate with the wheel 48 and module housing and provide successive angular cam detent positions that register cam surfaces opposite the pawl elements 70 in correspondence with the visible indicia on top of wheel 48.

The ratchet wheel 62 is formed of identical ratchet plates 64 which are assembled with predetermined angular offsets and held together with a common retainer pin such as 114 in FIG. 2. Several such retainer pins may be employed and the ratchet plate holes through which these pins are passed are carefully located so that each ratchet plate will be properly oriented in the ratchet wheel with their index stops in the desired angular relationships as shown for example in FIG. 15.

The ratchet plates 64 need not be identical and in fact may provide different unusually spaced index stops for particularly desired line spacings. For example, the index stops may be spaced to provide non-linear line spacings representative of a mathematical relationship.

The cable 43 runs within the channel 113 formed by removable channel housing 42 and is stretched over both pulley 80 in the control module 41 and a pulley (not shown) located at the upper end of channel housing 42. The cable 43 is connected into a closed loop with bracket 44 which is shaped in the form of a T. The crossbar segment 112 of bracket 44 has one end 115 firmly affixed to an end 116 of cable 43 while the other crossbar segment 118 is connected to the other end 120 of cable 43 through a controllable tension device 122.

The tension device 122 includes lever 46 which is pivotally connected at 124 to the crossbar segment 118. The lever 46 has an extension 126 which includes a post 128 to which the other end 120 of cable 68 is effectively connected through a tension spring 130. The extension 126 pivots between a release stop 132 and a tension stop 134. The lever exension 126 is bent towards tension stop 134. The lever extension 126 is bent towards tension stop 134 so that the lever extension 126 may engage the latter stop with a toggle (over center) action relative to the direction of the force exerted by spring 130. counterclockwise movement of lever 46 is accompanied by a tensioning of spring 130 to cause the cable 68 to tightly grip the pulley 80. When the lever is moved clockwise the spring tension is sufficiently released (without cable disengagement from the pulleys) to enable the cable 68 to slide over the pulley 80 even with the ratchet wheel 62 seated against a pawl element 70. The wall 136 of channel 42 terminates above beam 30 to form a longitudinal slot 137 along which bracket 44 travels as the drafting head 28 is moved.

An advantageous feature of the index device 40 resides in the ease with which different ratchet wheels 62 may be used in the control module 41. Tis This may be especially appreciated with reference to FIG. 4. The control module 41 shown in FIG. 4 shows the knob 84 provided with a central bore 140 which is sized to receive the ratchet wheel mounting shaft 82. Lock screw 85 assures firm connection between shaft 82 and knob 84. Shaft 82 passes freely through a bore 142 in a cylindrical cap 144, so that the knob 84, shaft 82 and ratchet wheel 62 form an integral rotatable assembly which may rotate relative to cap 144, The cap 144 is captured by module housing 98 with several latch bars 146, each of which engages an inwardly facing slot 148 in the wall 150 of housing 98. The ratchet program wheel assembly may be removed from module housing 98 by gripping the cap 144, twisting it counterclockwise to register the latch bar 146 with an axially oriented slot 152 and then lifting the assembly out of the module housing 98.

The ratchet program wheel 62 may be quickly replaced with another for different index spacing as desired. The friction coupling provided with friction discs 8686' assures that the ratchet program wheel 62 rotates in response to movements of cable 43. Easily disengageable couplings such as magnetic or splined or key shafts may be used to mount the ratchet wheel 62 to the shaft 82 for quick replacement.

One may appreciate from the foregoing description that the index spacing of the drafting head 28 may be entirely controlled with direct manual adjustment of the drafting head. The draftsman may continue to concentrate on his work sheet 26, after pausing but shortly to program his desired spacing by rotation of program wheel 48. Section lines may be drawn by directly advancing the drafting head downwardly in the direction of arrow 160 in FIG. 2 to thus rotate the ratchet program wheel 62 clockwise. As the ratchet wheel 62 rotates an actuated pawl element snaps into an index stop 66 with an audible click. Upon hearing this, the drafting head 28 is reversed opposite to the direction indicated by arrow 160 to seat the pawl element which produced the audible click against an index stop edge 66, at which point another section line may be drawn.

An advantageous feature of the index apparatus of this invention resides in the ability to commence index spacings from any desired region on the drafting board surface 24. In the embodiment in FIG. 2 this may be accomplished by moving the cable tension lever 46 to its spring tension release position (clockwise). The drafting head 28 is then moved to the desired location. The knob 84 is rotated to seat a pawl element 70 against an index stop 66. The lever 46 is then returned to its tensioning position (counterclockwise) after which section lines may be drawn with reference to the desired location.

FIG. 12 illustrates an alternate embodiment for a control module 41 to enable the operator to reference his section lines from any desired location. The drafting head 28 may be moved relative to the ratchet wheel 62 by lifting knob 84 against a spring bias to spearate the friction discs 8686. After the drafting head 28 is at its desired location, the knob 84 is released while maintaining a pawl element seated against an index stop.

The control module shown in FIG. 12 employs a coil spring 162 seated in a counter bore 164 of cap 144 between the cap and a low friction washer-bearing 166 on the ratchet wheel 62 to provide axial pressure between the friction discs 8686. The program mounting shaft 82 is provided with a through bore 168 which freely and slidingly receives a push button shaft 170. The push button shaft 170 extends down into bore 87 to seat upon the upper end of the bearing stud 76 and is captured in bore 87 with a retainer ring 172. The top of shaft 186 is provided with a cylindrical button shaped stop 174 whose stop surface 176 is selectively spaced from the upper surface 178 of knob 84. The entire ratchet program wheel assembly formed of knob 84, shaft 82 and the ratchet wheel 62 may be manually moved up against the pressure of spring 162 to separate friction discs 8686. The push button shaft 170 provides a convenient finger rest for lifting of the assembly, but may be dispensed with if desired. Without the push button shaft 170, the cap 144 serves as an axial stop when the ratchet wheel assembly is to be lifted.

The push button 174 is used to prevent lifting the drafting machine from the board 24.

FIG. 13 illustrates an alternate embodiment for the control module 41 by forming the ratchet program wheel of a generally axially wide gear segment 180. The index stops 182 are shaped in a similar manner as those on a ratchet plate 64 except that each stop extends in width over the entire axial length of the gear segment 180. A compound pawl 184 is employed in a similar manner as in the embodiment of FIG. 2 with a cam 72. The compound pawl 184, however, includes pawl elements 186.1, 186.2 and 186.3 which are of different lengths. Although the index spacing obtained by actuating a single pawl element 186 is determined by the angular spacings between successive index stops 182, the actuation of a pair of pawl elements186 by cam 72 provides intervals between lines similar to those illustrated in FIG. 1.

FIGS. 11 and 14 illustrate alternate embodiments for a ratchet wheel with a compound pawl in accordance with the invention. In FIG. 11 the ratchet program wheel 190 is a hollow cylinder with axially spaced circular rows of separated slots 192. The angular opposite sides 194-194' of slots 192 operate as index stops against which the pawl elements of a compound pawl are seated. The ratchet program wheel 190 is mounted with a bayonet engagement 196 on a cylindrical support 198.

The ratchet program wheel 200 shown in FIG. 14 is formed of a generally flat plate with upturned inclined segments 202 which serve as index stops. The index stops 202 are arranged in circular rows around the axis 204 of the ratchet wheel 200. A compound pawl 68 is operatively disposed in a generally horizontal manner for contact with index stops 202 upon actuation of cam 72.

As described with the operation of the embodiment of FIG. 2 the index lines are drawn by moving the drafting head down and then reversing its movement to seat against an index stop. FIG. 17 shows a control module embodiment where another compound pawl 68 is disposed on the opposite side of the axis of a ratchet program wheel 62 to enable the draftsman to generate index lines upwardly, i.e. from the bottom of the board 24. operation with the compound pawl 68' is obtained with a ratchet program wheel 62' having its index stops 66 facing clockwise, i.e. reversely from those shown in FIG. 2. The ratchet wheel 62 employed with a pair of compound pawls as illustrated in FIG. 17 may conveniently include ratchet plates with index stops orientations as shown in both FIGS. 2 and 17. Such ratchet plates may then be axially spaced opposite pawls 68-68 so that up or down indexing may be obtained as desired.

FIG. 25 schematically illustrates a reversing mechanism by which a draftsman may reverse the line spacing direction from downwardly as in FIG. 1 to upwardly. With the mechanism shown in FIG. 25 the drafting head 28 may be advanced upwardly along the direction of arrow 160' until an audible pawl element produced click is heard at which the drafting head motion is reversed to seat the pawl element against an index stop.

The cable 43 is wrapped around a pulley which is located below a cable coupler wheel 300. The cable coupler wheel 300 in turn is operatively coupled to a main coupler wheel 302 which is coaxially located with and below ratchet index program wheel 62 (not visible in the view of FIG. 25). The cable coupler wheel 300 may be coupled to the main coupler through either a single intermediate coupler 304 or a pair of serially connected intermediate couplers 306, 308. The couplers 304, 306 and 308 may be friction wheels or gears and are mounted on a lever 310. Lever 310 is mounted for pivot movement about the ratchet wheel rotational axis and includes an extension 312 on which wheel 304 is mounted. Couplers 304 and 306 remain in permanent engagement with themain coupler wheel 302 and thus also the ratchet control wheel, though their point of engagement may be rotated with pivot movement of lever 310.

In the illustrated position in FIG. 25, the coupler 304 provides for a downward line spacing in the direction of arrow and as described with reference to FIG. 1. By moving the lever 310 to a position at 312, the coupler 304 is disconnected and the couplers 306 and 308 now interconnect the drafting head 28 with the ratchet program wheel 62 through main coupler 302. Hence, at position 312 of lever 310 an upward indexing or line spacing may be obtained. The upward line spacing is accomplished by moving the drafting head 28 up, in the direction of arrow until an audible click or other indication of completed index movement is noticed, whereupon the drafting head is reversed in movement in the direction of arrow 160 to firmly seat a pawl element against an index stop.

Lever 310 may be conveniently employed to disenage the indexing device from the drafting head 28 by moving the lever 310 to a neutral position at 314. With the lever 310 at this neutral position 314 neither intermediate coupler 304 nor 308 is engaged with the cable coupler 300.

The line indexing device 40 according to this invention is particularly useful for dividing a line into a desired number of equal parts or proportional parts as determined by the programmed spacing. FIGS. 18 through 23 illustrate such use in conjunction with a calibrated plate 210 mounted on the drafting head 28 in place of straight edge 29 (shown in FIG. 1). The calibrated plate 210 is preferably made of transparent plastic to reveal the underlying drawing on work sheet 26 and is connected to the drafting head 28 with a standard mounting bracket 212.

The calibrated plate 210 is provided with a pair of intersecting mutually perpendicular side edges 214 and 216. The side edge 214 is calibrated with indicia lines such as 218, which, as shown by the registered columns 220.1, 220.2 and 220.3, indicate the number of index spacings between the first indicia line 218.1 and the remaining indicia lines 218. A

The columns 220 respectively correspond with selected index programs as obtained by rotation of the cam 72 in FIG. 2. The indicia between parentheses above the columns 240 relate to the indicia employed on the program control wheel 48.

Suppose, for example, that the vertical line 224 in FIG. 18 is to be divided into ten equal segments. After releasing the index device 40, such as by clockwise movement of lever 46 (see FIG. 1), the draftsman draws horizontal sketch lines 225-225 which respectively coincide with the ends 226226' of line 224. He then rotates the program control wheel 48 to a position where the column 220.1 labelled (.25) determines the index spacings. These column labels between parentheses refer to actual distances in inches between successive index lines, but could be replaced with arbitrary designations where such distance correlation cannot be established. The side edge 214 and its first indicia line 218.] (labelled O") is then located opposite the top end 226 of line 224 and a mark 228 is drawn opposite the indicia line 218.6 or the indicia of column 220.1 as shown in FIG. 19 and a light reference line is drawn through points 226, 226 and 228.

The protractor 34 of the drafting head 28 is then loosened to enable the drafting head to be rotated until the side edge 214 coincides with point 226 and side edge 216 is aligned with mark 228 while the corner 230 of the plate 210 lies on horizontal line 225'. A line 232 is drawn along side edge 234 as shown in FIGS. 20 and 21 and the protractor 34 is locked.

The drafting head 28 is now moved to align the straight edge 29 with point 226 as shown in FIG. 22. Lever 46 is moved counter clockwise to increase cable tension and bring the index device 40 into operation and the Y" beam 30 on the drafting instrument 20 is preferably locked to prevent movement. The index device is now actuated with intervals 234 marked off along line 232 as shown in FIG. 23 until the last line, which interconnects mark 228 with the intersection between line 232 and 225', is formed. The straight edge 29 is then returned to a horizontal position, the index device is released and horizontal lines 240 are drawn between the interval marks 234 and line 224 to obtain the desired ten equal divisions thereof.

One may appreciate that the described method and device for equal division of a line can be applied for different spacings such as proportional, harmonic and the like. The ratchet programmed wheel in cooperation with the compound. pawl can provide such spacings with desirable precision.

The indexing of the drafting head 28 has so far been described in conjunction with fixed predetermined index program wheels that establish specific, although selectable, index spacings. The control module 250 shown in FIG. 24 illustrates an index device capable of providing continuously adjustable line spacing. This is obtained by interposing an infinitely variable coupler 251 between the-pulley 66 and the ratchet program wheel 62.

The coupler 251 is formed of a friction drive wheel 252 operatively mounted between the axially upper surface 254 of the pulley 80 and a disc 256 mounted to the ratchet program wheel shaft 82'. The friction drive wheel 252 is formed of a ball bearing 258 whose outer race 260 is banded by a high friction material 262. The inner race 264 of bearing 258 is affixed to a control lead screw 266 which is mounted for movement in the directions indicated by double headed arrow 268. The control shaft 266 is mounted for rotation in a tapped hole 269 in the wall 270 of the control module housing 271. Hence, rotation by knob 272 enables the control lead screw 266 to be moved in the directions indicated by arrow 268 and thus adjust the operative location of the friction drive wheel 252.

For example, when the control lead screw 266 has been rotated to position the friction drive wheel 252 at location A only small movements of the drafting head 28 (and thus also rotation of the pulley 80) are needed to bring successive index stops on the program control wheel 62 into operation with a pawl element. Hence, with the friction drive wheel at position A, the line spacings may be quite small.

On the other hand when the friction drive wheel 252 is moved towards position B the line spacings become correspondingly wider since the drafting head must be moved a greater amount between successive index stops.

Operative contact of the friction control wheel 252 with pulley and disc 256 is assisted with a pair of spring bias assemblies 274274'. The spring bias assemblies 274 urge the pulley 80 and disc 256 towards each other, clamping the friction drive wheel 252 between them. Each spring bias assembly 274 is formed of a spring 276 seated between a wall of the control module 271 and a thrust washer 277. Each thrust washer 277 seats against a thrust bearing 278. The annular springs 276-276' are each mounted coaxially with axially and rotatably movable mounting shafts 280-280' respectively connected to the disc 256 and pulley 80. Sleeve bearings 282-282' (or ball bearings) are mounted in the walls of the control module to receive mounting shafts 280-280. Mounting shaft 280 is further provided with a key-extension 82'. This keyed fit enables the disc 256 to be spring biased against the friction control wheel 252 while maintaining engagement with the program control wheel 62. In addition the program wheel 62 may be easily replaced by simply lifting the installed unit out of engagement with the shaft 280 after removal of cap 144. A lowfriction thrust washer 284 is employed between the program control wheel 62 and the control module housing 271.

The control module 250 illustrated in FIG. 24 may utilize a ratchet program wheel as shown in the previous drawings with a compound pawl as described. The line spacing may still be conveniently obtained by the direct control of the drafting head with the additional advantage that index spacings determined by the program wheel may be effectively multiplied by the position control of the friction control wheel 252. The variable coupler 251 may be replaced with a multiple gear assembly wherein various gear ratios may be selected to vary the index spacings. The adjustment of line spacings may then be obtained at fixed accurately settable increments.

In the embodiment shown in FIG. 26 the compound pawl 68 is mounted on the crossbar 1 12 of the T shaped bracket 44. The pawl 68 thus moves along with the drafting head (not shown in FIG. 26). A rack 320 having index stops 322 is spaced parallel to the movement of the drafting machine head to which bracket 44 is attached. This enables the pawl elements 70, which are offset in a manner similar to FIG. 13, to engage the index stops 322. A cam 72 is operatively disposed on bracket 44 with respect to pawl 68 in a manner similar to the embodiment as shown in FIG. 2. The individual actuation of the pawl elements may provide a variable index spacing such as illustrated in FIG. 1.

The portion of rack 324 shown in FIG. 27 is conveniently employed with the embodiment of FIG. 26. The rack 324 is mounted like rack 320 parallel with the line of travel of compound pawl 68 but is furthermore mounted for rotation about axis 326 which is parallel with the line of travel of compound pawl 68. Rack 324 is provided with parallel angularly spaced rows such as 328 and 330 of index stops 322. The index stops in row 328 may be difi'erently spaced from those in row 330 to provide correspondingly different line index spacings of the drafting head upon rotation of rack 324.

Alternatively, the index stops, in row 330, for example, may be reversely oriented to those in row 328 to provide up-indexing of the drafting head in conjunction with a compound pawl which also faces operatively reversely from the pawl shown in FIG. 26.

Having thus described an index device for use with drafting instruments the many advantages may be appreciated. The draftsman may accomplish the desired line indexing with excellent precision and in a conveniently employable manner. The indexing device may be adapted for horizontal indexing. The versatile programming of line spacings enhances draftsman control. Tedious efforts for extensive line spacing work are reduced for improved draftsman efficiency.

What is claimed is: i

1. An index device for controlling index positions of a drafting instrument drafting head which is mounted for movement along orthogonal directions comprising a ratchet component having successively located index stops, a pawl component, one of said components being mounted for movement relative to the other component, with said other component mounted at a fixed position on the drafting instrument, said pawl component being operatively disposed to seat against the index stops upon a movement between the ratchet component and the pawl component in a first direction, said pawl component and index stops being selectively oriented to enable free movement between the pawl component and the ratchet component in a second direction opposite to said first direction,

means for adjustably coupling the drafting head to one of said components, and cause relative movement between the ratchet and pawlcomponents in correspondence with drafting head movement, said coupling means enabling said drafting head to move free of index stops in one selected orthogonal direction while limiting movement of the drafting head to successive index positions in an opposite direction from said one selected orthogonal direction,

said coupling means including a flexible cable loop stretched along said one orthogonal direction and coupled to said drafting head and said one component to obtain relative movement between the components in correspondence with drafting head movements.

2. The index device as claimed in claim 1 wherein said ratchet component is formed in the shape of a wheel operatively driven into rotation by said cable loop and wherein said pawl component is formed of a compound pawl having a plurality of pawl elements, said pawl elements extending in cantilever fashion towards the ratchet wheel and individually movable for engagement with index stops on the ratchet wheel.

3,. The index device as claimed in claim 1 wherein said pawl component is effectively mounted on the cable loop for coupling to the drafting head, said ratchet component being formed of a longitudinal ratchet member having index stops distributed along the length of the ratchet member, said ratchet member being mounted parallel with a selected direction of movement of the drafting head for operative engagement by the cable mounted pawl.

4. The index device as claimed in claim 3 wherein said longitudinal ratchet member has angularly distributed longitudinal rows of index stops of different spacings and is mounted for rotation about a longitudinal axis parallel with said selected direction of movement of the drafting head to enable said pawl to engage a desired longitudinal row of index stops.

5. The index device as claimed in claim 3 wherein said pawl component is formed of a compound pawl having pawl elements of different operative lengths to provide correspondingly different index spacings of the drafting head and means for bringing selected ones of said pawl elements into operative engagement with the index stops on the longitudinal ratchet member.

6. An index device for controlling index positions of a drafting instrument drafting head which is mounted for movement along orthogonal directions comprising a cable loop stretched parallel to one of said orthogonal directions and operatively coupled to the drafting head for movement of the cable in response to motions of the drafting head along said one orthogonal direction, an index control module including a rotationally mounted ratchet wheel having index stops distributed about the ratchet wheel axis of rotation, said ratchet wheel being effectively coupled to the cable loop for wheel rotation in response to drafting head movements along said one orthogonal direction, a pawl operatively disposed with respect to the ratchet wheel to seat against said index stops and limit a selected direction of rotational movement of the ratchet wheel in correspondence with pawl-index stops engagements, said index stops and pawl further being selectively oriented to permit free ratchet wheel rotation in an angular direction opposite to said selected direction of rotational movement of the ratchet wheel, whereby said drafting head may be moved to successive index position with direct manipulation of said drafting head.

7. The index device as claimed in claim 6 and further including means interposed between the ratchet wheel and the cable loop for selecting the direction of index movements of the drafting head.

8. The index device as claimed in claim 7 wherein said index movement direction selecting means includes a first rotational coupler movably mounted to operatively couple the ratchet wheel to the cable loop,

a pair of series engaged rotational couplers movably mounted to operatively couple the ratchet wheel to the cable loop, and

means for moving said first rotational coupler or said pair of series engaged rotational couplers into operative engagement between the ratchet wheel and cable loop to correspondingly control the direction of index movement of the drafting head.

9. The index device as claimed in claim 7 wherein said index movement direction selecting means includes a pair of pawls operatively disposed to seat against index stops, said pawls being oppositely oriented to provide index movements with opposite rotational movements of the ratchet wheel, and means for controlling the operative engagement of said pawls with said ratchet wheel index stops.

10. The index device as claimed in claim 6 and further including means for varying the index spacings of the drafting head.

11. The index device as claimed in claim 10 wherein said index spacing varying means includes a compound pawl having a plurality of pawl elements, said pawl elements being individually movable towards the index stops to correspondingly vary the index spacings, and a cam mounted adjacent the pawl elements to selectively urge individual ones of said pawl elements into engagement with index stops.

12. The index device as claimed in claim wherein said index spacing varying means includes a variable speed ratio changer operatively interposed between said ratchet wheel and said cable loop.

13. The index device as claimed in claim 12 and further including a pulley rotationally mounted to the control module and operatively engaged by the cable loop, and wherein the variable speed ratio changer includes a disc coaxially mounted with the ratchet wheel for rotation therewith, said disc having an axial drive surface spaced from the pulley in selected overlapped relationship, and a rotationally mounted drive wheel located between the pulley and the disc, said drive wheel being in contact with the disc drive surface and effectively and axial surface of the pulley to rotatably couple the pulley to the ratchet wheel, said drive wheel further being mounted for movement parallel with said drive surface and axial pulley surface to vary the coupling between the cable and the ratchet wheel and correspondingly effectively vary the index spacings determined by successive index stops.

14. An indexing device for controlling index positions of a drafting instrument line former which is mounted for movement along predetermined directions on the drafting instrument comprising means operatively coupled to the line former to selectively limit line former originating movement to predetermined index positions along a selected direction, said index movement limiting means further including a rotatably mounted ratchet wheel having index stops, and a pawl operatively disposed .with respect to the ratchet wheel and a cable oriented along said selected direction, said cable being coupled to the line former and the ratchet wheel to provide ratchet wheel rotation in response to movement of the line former along the selected direction, said ratchet wheel being provided with the index stops which are distributed about the rotational axis of the ratchet wheel, said index stops being operatively engaged by the pawl to provide index movement limits upon rotation of the ratchet wheel in one direction while permitting free ratchet wheel rotational movement in an opposite direction,

means operatively interposed between the line former and the index movement limiting means for effectively releasing the coupling between the cable and the ratchet wheel to enable movement of the line former relative to the index movement limiting means to commence index spacings from any desired location along said one selected direction with any desired location of the line former along said one selected direction.

15. The indexing device as claimed in claim 14 wherein said releasing means includes a cable tension adjuster mounted in series with the cable and having a first operative position for increased cable tension with line former index movement and a second operative position for reduced cable tension enabling overriding relative line former movement.

16. The indexing device as claimed in claim 15 wherein said releasing means includes a friction clutch coaxially located with the ratchet wheel, said friction clutch being axially disengageable to enable relative movement between the index stops and the line former.

17. The indexing device as claimed in claim 14 and further including a pulley coaxially located with said ratchet wheel and with said cable operatively wrapped around the pulley and wherein said releasing means includes a friction clutch axially interposed between the ratchet wheel and the pulley to enable relative motion between the line former and the index stops.

18. An indexing device for a drafting instrument having a line former which is mounted for movement along orthogonal directions comprising a flexible cable aligned with one of said orthogonal directions and operatively coupled to the line former to provide cable drive movement in correspondence with motion of the line former along said one direction,

a ratchet wheel mounted for rotation about an axis, said ratchet wheel having index stops distributed about the ratchet wheel axis,

said flexible cable being operatively coupled with the ratchet wheel to cause rotation thereof in correspondence with movement of the line former along said one orthogonal direction,

a compound pawl formed of a plurality of individually adjustable pawl elements, said compound pawl being operatively disposed with the ratchet wheel to enable said pawl elements to be selectively individually seated against the index stops,

said index stops and said individually adjustable pawl elements further being selectively located relative to one another to provide different angular index positions of the ratchet wheel in correspondence with individual operatively adjusted pawl elements,

means for programming the operative engagement of selected pawl elements with respect to the index stops to determine the magnitude of the angular index movement of the ratchet wheel in correspondence with the programmed engaged pawl elements, and

means for adjusting the angular position of the ratchet wheel relative to a desired location of the line former along said one orthogonal direction and register the index stops of the ratchet wheel with the desired location of the line former to commence line indexing with reference to the desired line former location.

19. The indexing device as claimed in claim 18 wherein said ratchet wheel angular position adjusting means include a cable partial tension releasing coupler operatively engaged with the cable, said coupler having a tension releasing position to enable relative movement between the ratchet wheel and the cable.

20. The indexing device as claimed in claim 18 wherein said ratchet wheel angular position adjusting means includes a releasable friction clutch operatively interposed betseen the flexible cable and the ratchet wheel.

21. An indexing device for controlling index positions of a drafting instrument line former which is mounted for movement along orthogonal directions on the drafting instrument comprising a ratchet wheel mounted for rotation about an axis and having pawl stops angularly distributed about the ratchet wheel axis with predetermined angular spacings,

a compound pawl formed of a plurality of individually engagcable adjustable pawl elements, said compound pawl being operatively disposed on with the ratchet wheel to enable said pawl elements to be selectively individually seated against pawl stops,

said pawl stops and said individually adjustable pawl elements further being selectively aligned with one another to provide different angular index positions of the ratchet wheel in correspondence with individual operative engagement of the pawl elements,

means for programming the operative engagement of selected pawl elements with respect to the pawl stops and to determine the magnitude of the angular index movement of the ratchet wheel in correspondence with the programmed engaged pawl elements,

and means for operatively coupling the ratchet wheel to the line generator to provide index movement thereof with a magnitude which is determined by the engaged pawl element.

22. The indexing device as claimed in claim 21 wherein the compound pawl is formed of a pawl retainer and spaced parallel spring pawl bars held by the pawl retainer and-extending in cantilever fashion therefrom towards the pawl stops to selectively seat against the pawl stops in response to said programming means.

23. The indexing device as claimed in claim 22 wherein the spaced parallel spring pawl bars terminate at their cantilever ends along a common line and wherein the pawl stops on the ratchet wheel are arranged in spaced circular rows with the spacing between rows commensurate with the spacings between the spring pawl bars and with the pawl stops of different rows being angularly displaced with one another to provide different angular index movements in correspondence with the actuation of the programming means.

24. The indexing device as claimed in claim 22 wherein the spaced parallel spring bars terminate at different operative cantilever ends commensurate with desired angular index movements of the ratchet wheel.

25. The indexing device as claimed in claim 24 wherein the pawl stops on the ratchet wheel are arranged in a common circular row about the ratchet wheel axis and extend in operative width for a distance sufficient to enable the spaced pawl bars to seat against the pawl stops upon actuation of the programming means.

26. The indexing device as claimed in claim 21 wherein the programming means includes a moveably mounted cam having cam surfaces for contact with the respective pawl elements, said cam surfaces being shaped to select operative engagement of pawl elements with the pawl stops in response to cam movement.

27. ln an index device for controlling index positions of a drafting head for a drafting instrument, the improvement comprising a ratchet wheel operatively coupled to the drafting head for being driven into rotation in correspondence with movements of the drafting head, said ratchet wheel having index stops distributed about the axis of rotation of the ratchet wheel, a compound pawl having a plurality of individually movable pawl elements of selected different lengths, and means for moving individual ones of said pawl elements for engagement with index stops to program different index spacings of the drafting head in correspondence with different pawl elements brought into engagement.

28. The improved index device as claimed in claim 27 wherein the ratchet wheel is formed of a hollow cylinder having a plurality of circumferentially located axially spaced rows of circumferentially separated slots, with the pawl elements being individually disposed in operative relationship with a selected row of slots to engage walls thereof for index spacings of the drafting head.

29. The improved index device as claimed in claim 27 wherein said ratchet wheel is in the form of a generally flat disc having radially spaced annular rows of axially raised protrusions shaped for engagement by the pawl elements. 

1. An index device for controlling index positions of a drafting instrument drafting head which is mounted for movement along orthogonal directions comprising a ratchet component having successively located index stops, a pawl component, one of said components being mounted for movement relative to the other component, with said other component mounted at a fixed position on the drafting instrument, said pawl component being operatively disposed to seat against the index stops upon a movement between the ratchet component and the pawl component in a first direction, said pawl component and index stops being selectively oriented to enable free movement between the pawl component and the ratchet component in a second direction opposite to said first direction, means for adjustably coupling the drafting head to one of said components, and cause relative movement between the ratchet and pawl components in correspondence with drafting head movement, said coupling means enabling said drafting head to move free of index stops in one selected orthogonal direction while limiting movement of the drafting head to successive index positions in an opposite direction from said one selected orthogonaL direction, said coupling means including a flexible cable loop stretched along said one orthogonal direction and coupled to said drafting head and said one component to obtain relative movement between the components in correspondence with drafting head movements.
 2. The index device as claimed in claim 1 wherein said ratchet component is formed in the shape of a wheel operatively driven into rotation by said cable loop and wherein said pawl component is formed of a compound pawl having a plurality of pawl elements, said pawl elements extending in cantilever fashion towards the ratchet wheel and individually movable for engagement with index stops on the ratchet wheel.
 3. The index device as claimed in claim 1 wherein said pawl component is effectively mounted on the cable loop for coupling to the drafting head, said ratchet component being formed of a longitudinal ratchet member having index stops distributed along the length of the ratchet member, said ratchet member being mounted parallel with a selected direction of movement of the drafting head for operative engagement by the cable mounted pawl.
 4. The index device as claimed in claim 3 wherein said longitudinal ratchet member has angularly distributed longitudinal rows of index stops of different spacings and is mounted for rotation about a longitudinal axis parallel with said selected direction of movement of the drafting head to enable said pawl to engage a desired longitudinal row of index stops.
 5. The index device as claimed in claim 3 wherein said pawl component is formed of a compound pawl having pawl elements of different operative lengths to provide correspondingly different index spacings of the drafting head and means for bringing selected ones of said pawl elements into operative engagement with the index stops on the longitudinal ratchet member.
 6. An index device for controlling index positions of a drafting instrument drafting head which is mounted for movement along orthogonal directions comprising a cable loop stretched parallel to one of said orthogonal directions and operatively coupled to the drafting head for movement of the cable in response to motions of the drafting head along said one orthogonal direction, an index control module including a rotationally mounted ratchet wheel having index stops distributed about the ratchet wheel axis of rotation, said ratchet wheel being effectively coupled to the cable loop for wheel rotation in response to drafting head movements along said one orthogonal direction, a pawl operatively disposed with respect to the ratchet wheel to seat against said index stops and limit a selected direction of rotational movement of the ratchet wheel in correspondence with pawl-index stops engagements, said index stops and pawl further being selectively oriented to permit free ratchet wheel rotation in an angular direction opposite to said selected direction of rotational movement of the ratchet wheel, whereby said drafting head may be moved to successive index position with direct manipulation of said drafting head.
 7. The index device as claimed in claim 6 and further including means interposed between the ratchet wheel and the cable loop for selecting the direction of index movements of the drafting head.
 8. The index device as claimed in claim 7 wherein said index movement direction selecting means includes a first rotational coupler movably mounted to operatively couple the ratchet wheel to the cable loop, a pair of series engaged rotational couplers movably mounted to operatively couple the ratchet wheel to the cable loop, and means for moving said first rotational coupler or said pair of series engaged rotational couplers into operative engagement between the ratchet wheel and cable loop to correspondingly control the direction of index movement of the drafting head.
 9. The index device as claimed in claim 7 wherein said index movement direction selecting means includes a pair of pawls operatively disposed to seat agAinst index stops, said pawls being oppositely oriented to provide index movements with opposite rotational movements of the ratchet wheel, and means for controlling the operative engagement of said pawls with said ratchet wheel index stops.
 10. The index device as claimed in claim 6 and further including means for varying the index spacings of the drafting head.
 11. The index device as claimed in claim 10 wherein said index spacing varying means includes a compound pawl having a plurality of pawl elements, said pawl elements being individually movable towards the index stops to correspondingly vary the index spacings, and a cam mounted adjacent the pawl elements to selectively urge individual ones of said pawl elements into engagement with index stops.
 12. The index device as claimed in claim 10 wherein said index spacing varying means includes a variable speed ratio changer operatively interposed between said ratchet wheel and said cable loop.
 13. The index device as claimed in claim 12 and further including a pulley rotationally mounted to the control module and operatively engaged by the cable loop, and wherein the variable speed ratio changer includes a disc coaxially mounted with the ratchet wheel for rotation therewith, said disc having an axial drive surface spaced from the pulley in selected overlapped relationship, and a rotationally mounted drive wheel located between the pulley and the disc, said drive wheel being in contact with the disc drive surface and effectively and axial surface of the pulley to rotatably couple the pulley to the ratchet wheel, said drive wheel further being mounted for movement parallel with said drive surface and axial pulley surface to vary the coupling between the cable and the ratchet wheel and correspondingly effectively vary the index spacings determined by successive index stops.
 14. An indexing device for controlling index positions of a drafting instrument line former which is mounted for movement along predetermined directions on the drafting instrument comprising means operatively coupled to the line former to selectively limit line former originating movement to predetermined index positions along a selected direction, said index movement limiting means further including a rotatably mounted ratchet wheel having index stops, and a pawl operatively disposed with respect to the ratchet wheel and a cable oriented along said selected direction, said cable being coupled to the line former and the ratchet wheel to provide ratchet wheel rotation in response to movement of the line former along the selected direction, said ratchet wheel being provided with the index stops which are distributed about the rotational axis of the ratchet wheel, said index stops being operatively engaged by the pawl to provide index movement limits upon rotation of the ratchet wheel in one direction while permitting free ratchet wheel rotational movement in an opposite direction, means operatively interposed between the line former and the index movement limiting means for effectively releasing the coupling between the cable and the ratchet wheel to enable movement of the line former relative to the index movement limiting means to commence index spacings from any desired location along said one selected direction with any desired location of the line former along said one selected direction.
 15. The indexing device as claimed in claim 14 wherein said releasing means includes a cable tension adjuster mounted in series with the cable and having a first operative position for increased cable tension with line former index movement and a second operative position for reduced cable tension enabling overriding relative line former movement.
 16. The indexing device as claimed in claim 15 wherein said releasing means includes a friction clutch coaxially located with the ratchet wheel, said friction clutch being axially disengageable to enable relative movement between the index stops and the line former.
 17. The indeXing device as claimed in claim 14 and further including a pulley coaxially located with said ratchet wheel and with said cable operatively wrapped around the pulley and wherein said releasing means includes a friction clutch axially interposed between the ratchet wheel and the pulley to enable relative motion between the line former and the index stops.
 18. An indexing device for a drafting instrument having a line former which is mounted for movement along orthogonal directions comprising a flexible cable aligned with one of said orthogonal directions and operatively coupled to the line former to provide cable drive movement in correspondence with motion of the line former along said one direction, a ratchet wheel mounted for rotation about an axis, said ratchet wheel having index stops distributed about the ratchet wheel axis, said flexible cable being operatively coupled with the ratchet wheel to cause rotation thereof in correspondence with movement of the line former along said one orthogonal direction, a compound pawl formed of a plurality of individually adjustable pawl elements, said compound pawl being operatively disposed with the ratchet wheel to enable said pawl elements to be selectively individually seated against the index stops, said index stops and said individually adjustable pawl elements further being selectively located relative to one another to provide different angular index positions of the ratchet wheel in correspondence with individual operatively adjusted pawl elements, means for programming the operative engagement of selected pawl elements with respect to the index stops to determine the magnitude of the angular index movement of the ratchet wheel in correspondence with the programmed engaged pawl elements, and means for adjusting the angular position of the ratchet wheel relative to a desired location of the line former along said one orthogonal direction and register the index stops of the ratchet wheel with the desired location of the line former to commence line indexing with reference to the desired line former location.
 19. The indexing device as claimed in claim 18 wherein said ratchet wheel angular position adjusting means include a cable partial tension releasing coupler operatively engaged with the cable, said coupler having a tension releasing position to enable relative movement between the ratchet wheel and the cable.
 20. The indexing device as claimed in claim 18 wherein said ratchet wheel angular position adjusting means includes a releasable friction clutch operatively interposed betseen the flexible cable and the ratchet wheel.
 21. An indexing device for controlling index positions of a drafting instrument line former which is mounted for movement along orthogonal directions on the drafting instrument comprising a ratchet wheel mounted for rotation about an axis and having pawl stops angularly distributed about the ratchet wheel axis with predetermined angular spacings, a compound pawl formed of a plurality of individually engageable adjustable pawl elements, said compound pawl being operatively disposed on with the ratchet wheel to enable said pawl elements to be selectively individually seated against pawl stops, said pawl stops and said individually adjustable pawl elements further being selectively aligned with one another to provide different angular index positions of the ratchet wheel in correspondence with individual operative engagement of the pawl elements, means for programming the operative engagement of selected pawl elements with respect to the pawl stops and to determine the magnitude of the angular index movement of the ratchet wheel in correspondence with the programmed engaged pawl elements, and means for operatively coupling the ratchet wheel to the line generator to provide index movement thereof with a magnitude which is determined by the engaged pawl element.
 22. The indexing device as claimed in claim 21 wherein thE compound pawl is formed of a pawl retainer and spaced parallel spring pawl bars held by the pawl retainer and extending in cantilever fashion therefrom towards the pawl stops to selectively seat against the pawl stops in response to said programming means.
 23. The indexing device as claimed in claim 22 wherein the spaced parallel spring pawl bars terminate at their cantilever ends along a common line and wherein the pawl stops on the ratchet wheel are arranged in spaced circular rows with the spacing between rows commensurate with the spacings between the spring pawl bars and with the pawl stops of different rows being angularly displaced with one another to provide different angular index movements in correspondence with the actuation of the programming means.
 24. The indexing device as claimed in claim 22 wherein the spaced parallel spring bars terminate at different operative cantilever ends commensurate with desired angular index movements of the ratchet wheel.
 25. The indexing device as claimed in claim 24 wherein the pawl stops on the ratchet wheel are arranged in a common circular row about the ratchet wheel axis and extend in operative width for a distance sufficient to enable the spaced pawl bars to seat against the pawl stops upon actuation of the programming means.
 26. The indexing device as claimed in claim 21 wherein the programming means includes a moveably mounted cam having cam surfaces for contact with the respective pawl elements, said cam surfaces being shaped to select operative engagement of pawl elements with the pawl stops in response to cam movement.
 27. In an index device for controlling index positions of a drafting head for a drafting instrument, the improvement comprising a ratchet wheel operatively coupled to the drafting head for being driven into rotation in correspondence with movements of the drafting head, said ratchet wheel having index stops distributed about the axis of rotation of the ratchet wheel, a compound pawl having a plurality of individually movable pawl elements of selected different lengths, and means for moving individual ones of said pawl elements for engagement with index stops to program different index spacings of the drafting head in correspondence with different pawl elements brought into engagement.
 28. The improved index device as claimed in claim 27 wherein the ratchet wheel is formed of a hollow cylinder having a plurality of circumferentially located axially spaced rows of circumferentially separated slots, with the pawl elements being individually disposed in operative relationship with a selected row of slots to engage walls thereof for index spacings of the drafting head.
 29. The improved index device as claimed in claim 27 wherein said ratchet wheel is in the form of a generally flat disc having radially spaced annular rows of axially raised protrusions shaped for engagement by the pawl elements. 